The present invention relates to a control circuit and a control method of controlling the rotation frequency of a spindle in an optical disc drive, and more particularly, to a control circuit and a control method of controlling the rotation frequency of a spindle in an optical disc drive through reducing a frequency difference between output signals respectively corresponding to different disc rotation modes.
There are two different operation modes for an optical disc drive to access optical discs, as is well known. The first operation mode is a constant linear velocity (CLV) mode and the second operation mode is a constant angular velocity (CAV) mode. According to different requirements, the optical disc drive applies a different mode to read or write data on the disc.
Unfortunately, control methods of the spindle are also different for these two operation modes. In CAV mode, a Hall sensor detects the rotation frequency of the spindle and the servo system generates a rotation control signal to control the spindle rotation frequency to lie between 10 Hz to 100 Hz. In CLV mode, the rotation frequency is detected through a wobble signal read by the pick-up head, or through an RF signal, and is then divided by a frequency divider. The rotation control signal controls the spindle to rotate with a frequency approximately 1 kHz. Because a run-out effect has to be considered in CLV mode, the rotation frequency in CLV mode cannot be reduced below 1 kHz, otherwise the run-out effect will cause data error when the optical disc drive accesses the optical disc.
Therefore, the rotation frequencies of the spindle are different in each operation mode, and subsequently, when the optical disc drive changes from CLV mode to CAV mode, the spindle has to reduce the rotation frequency of the CLV mode to match the rotation frequency of the CAV mode before mode switching can occur. Similarly, when the optical disc drive changes from CAV mode to CLV mode, the spindle has to increase the rotation frequency of the CAV mode to match the rotation frequency of the CLV mode before mode switching can occur.
Please refer to FIG. 1. FIG. 1 is a block diagram of a spindle controller 100 according to the related art. As the dotted line shows, the spindle controller 100 includes a frequency/phase detector 130, a proportion-integration (PI) controller 140, a mixer 150, a pulse-width modulation (PWM) controller 160, and a digitally modulated output low pass filter (DMOLPF) 170. As discussed above, a wobble signal W is divided by the frequency divider 110a with a divisor N to monitor the rotation frequency in the CLV mode (the frequency is divided so it approaches 1 kHz). Similarly, a detecting signal FG of spindle rotation in the CAV mode is also divided with a divisor K to monitor the rotation frequency in the CAV mode (the frequency is divided so it approaches 10 Hz-100 Hz). The multiplexer 120 selects one input signal as the output, according to the mode the optical disc drive is operating in.
For example, in the CLV mode, the multiplexer 120 selects the input route of the wobble signal W, and outputs a rotation control signal SCONT corresponding to the rotation frequency of the spindle. In CAV mode, the multiplexer 120 selects the input route of the detecting signal FG. Next, the frequency/phase detector 130 compares the rotation control signal SCONT with a reference clock CREF to generate a frequency error signal EF and a phase error signal EP according to the rotation control signal SCONT. The PI controller 140 receives the frequency error signal EF and the phase error signal EP and outputs a corrective signal SCORR to the closed-loop architecture including the mixer 150, the PWM controller 160, and the DMOLPF 170. The closed loop architecture processes the corrective signal SCORR to generate a driving-control signal SD to control the spindle rotation frequency.
Because the frequencies of the two inputs of the multiplexer 120 differ by a factor of ten, when the mode switch occurs, the multiplexer 120 switches the input route from one input to the other, resulting in the frequency of the output signal (the rotation control signal SCONT) changing rapidly and sharply. The significant frequency change of the rotation control signal SCONT introduces added design complexity to the control system, thereby necessitating the consideration of more parameters when stability during adjustment procedures has to be taken into account.